Apparatus for providing a protective spark gap for a d.c. powerline



3,413,524 OTECTIVE SPARK RLINE 13, 1965 D. TRAIN APPARATUS FOR PROVIDING A GAP FOR A D C P Filed July Nov. 26, 1968 United States Patent 3,413,524 APPARATUS FOR PROVIDING A PROTECTIVE SPARK GAP FOR A D.C. POWERLINE David Train, Stafford, England, assignor to The English Electric Company Limited, London, England, a British company Filed July 13, 1965, Ser. No. 471,552 Claims priority, application Great Britain, July 14, 1964, 28,923/64, Patent 1,080,623 8 Claims. (Cl. 31769) ABSTRACT OF THE DISCLOSURE A protective device for protecting a D.C. powerline from overvoltages has a triggatron and a spark gap connected in parallel between the powerline and earth. The triggat-ron has two main electrodes, one connected to the powerline and the other to earth, with a gap between them; and it also has a trigger electrode spaced from one of the main electrodes to give a trigger gap. A resistor is connected in circuit in series with the spark gap, and the trigger electrode is connected to this circuit so that, when a surge voltage high enough to break down the spark gap occurs, there is a voltage difference between the main electrode and the trigger electrode due to the resistor; this voltage difference appears across the trigger gap causing it to spark over; this causes breakdown of the gap between the two main electrodes, so that the overvoltage on the line is discharged to earth through the two main electrodes.

According to the present invention, apparatus for pro viding a protective spark gap for a powerline comprises a triggatron and means defining at least one spark gap connected in parallel between the powerline and earth, the triggatron having a first electrode connected to the powerline and a second electrode spaced from the first electrode and connected directly or indirectly to earth. At least one of the electrodes carries a trigger electrode facing the gap between the electrodes, the trigger electrode being insulated from the said electrode, by which it is carried, to provide a gap therebetween, and being connected to a tapping on a resistor in series with the spark gap or gaps.

A preferred form of the invention will now be described by way of example with reference to the accompanying drawings, of which:

FIG. 1 shows a diagrammatic view of a protective spark gap, and

FIG. 2 shows an enlarged sectional view of part of FIG. 1.

Referring to FIG. 1, an assembly of electrodes 11, hereinafter referred to as a triggatron, and means, generally indicated at 12, defining at least one spark gap 22 are connected in parallel between a D.C. powerline 13 and an earthed line 14.

The triggatron 11 includes two carbon main electrodes 15, 16 which are connected respectively to the D.C.

powerline 13 and to the earthed line 14. The main electrodes 15, 16 are of cylindrical shape and have hemispherical ends. They are arranged in such a way that the axes of the main electrodes and the line joining the centres of the two electrodes are mutually at right angles. Trigger electrode assemblies 17, 18 are mounted in the respective main electrodes 15, 16 and are coaxial with the line joining the centres of the main electrodes. Trigger electrodes 19, 20, which form part of the assemblies 17, 18, respectively, face each other across the spark gap 21 and are insulated from the main electrodes 15, 16.

The spark gap 22 is mounted within a sealed porcelain "ice housing (indicated diagrammatically by a chain line). The spark gap 22 is connected on one side to a high-voltage resistor 23, which is in turn connected to the D.C. powerline 13, and on the other side to a low-voltage resistor 24, which is connected to the earthed line 14. The resistors 23 and 24 are shown mounted within the sealed porcelain housing. The high-voltage resistor 23 is tapped by a tapping 25 connected to trigger electrode 19; similarly the low-voltage resistor 24 is tapped by a tapping 26 connected to trigger electrode 20.

Referring now to FIG. 2, the trigger electrode assembly 18 mounted in main electrode 16 will be described, but it will be understood that the arrangement of the other trigger electrode assembly 17 is substantially identical.

The trigger electrode assembly 18 includes an insulating plug 30 screwed into a tapped hole in the carbon main electrode 16. The plug 30 is fitted with a brass insert 31, and has a collet chuck 32 operating inside it. The trigger electrode 20 is made from tungsten rod and is held by the collet chuck 32. The trigger electrode 20 is finished flush with the surface of main electrode 16 adjacent the spark gap 21. A ceramic sleeve 33 is cemented to the trigger electrode 20 at the end of the sleeve remote from spark gap 21, and is flush with the surface of main electrode 16 at its other end. A terminal (not shown) is attached to the collet chuck 32 by means of a screw thread 34 and is connected to the tapping point 26 on the lowvoltage resistor 24.

Although in the preferred form of the invention the main electrodes 15, 16 (FIG. 1) are of cylindrical shape and at right angles to one another, they may be of any shape and in any configuration which gives a substantially uniform electric field in the spark gap 21; moreover, although the high-voltage and low-voltage tapping resistors are described as located in the sealed porcelain housing, they may be outside the sealed porcelain housing. Also both trigger electrodes 19, 20 may be triggered from tappings on a single resistor, which may be on either side of the spark gap 22. In addition there may be only one trigger electrode, which may be mounted in either main electrode and triggered from a tapping on a resistor located on either side of the spark gap 22. In all cases the resistors may be mounted inside or outside the sealed porcelain housing. Although shown in FIG. 1 as a single spark gap, the spark gap 22 may comprise multiple gaps in series.

Instead of the sparking ends of the trigger electrodes being mounted flush with the surfaces of the main electrodes, they may be withdrawn within the bodies of the main electrodes.

In operation, a sufficiently high surge voltage on line 13 will cause the spark gap 22 to break down and a current will flow between line 13 and the earthed line 14, passing through the high-voltage resistor 23, across the spark gap 22 and through the low-voltage resistor 24. Thus as a result of the voltage drops in the resistors 23, 24, voltages dependent on the positions of tappings 25, 26, will exist between trigger electrode 19 and main electrode 15 and between trigger electrode 20 and main electrode 16. These voltages will cause the trigger electrodes to spark over to their cor-responding main electrodes, which in turn will cause breakdown of the spark gap 21, so that the voltages on the line 13 is discharged to earth between the main electrodes 15, 16.

It will be appreciated that a particular voltage causes a spark gap to break down, the magnitude of the voltage being dependent upon the atmospheric conditions within the spark gap. Consequently, mounting the spark gap 22 within the sealed porcelain housing prevents variations of the atmospheric conditions within the spark gap 22 and causes the spark gap 22 to break down at a constant voltage.

Suitable blower means, such as a fan driven from a suitable source of power, e.g., an electric motor, may be provided to cause a draught of air to flow through the spark gap 21 of the triggatron 11. The draught of air, which may be flowing at -15 ft./sec., removes dust from the surface of the electrodes and thereby reduces the danger of spurious flash over within the spark gap 21.

It is to be understood that the apparatus of the present invention is particularly suitable for providing a protective spark gap for a DC. powerline.

It has been found that the use of a triggatron allows the spark gap 21 to be larger than it would be for a simple two-electrode gap, thus reducing the risk of spurious opperation due to atmospheric conditions.

With the arrangement of FIG. 1 in which a trigger electrode is mounted in each main electrode, the triggatron will work equally well with voltages of either polarity.

What I claim as my invention and desire to secure by Letters Patents is:

1. Apparatus for providing a protective spark gap for a DC. powerline, including a triggatron and spark gap means connected in parallel with one another between the DC. powerline and earth, the triggatron having a first rnain electrode connected to the DO powerline and a second main electrode spaced from the first main electrode to provide a first gap therebetween and connected to earth, at least one of the main electrodes carrying a trigger electrode adjacent to said first gap, the trigger electrode being insulated from the said main electrode by which it is carried to provide a second gap therebetween, and resistor means connected in series with said spark gap means between the DC. powerline and earth, the trigger electrode being connected to a tapping on said resistor means, so that a flow of current across said spark gap means causes the DC. line to discharge to earth via the main electrodes.

2. Apparatus for providing a protective spark gap for a DC. powerline as claimed in claim 1, wherein the axes of the first and second main electrodes and the line joining the centres of the first and second main electrodes are mutually perpendicular.

3. Apparatus for providing a protective spark gap for a DC. powerline as claimed in claim 2, wherein said resistor means includes a resistor connected between said spark gap means and the DC. powerline, and said trigger electrode is carried by said first main electrode and connected to a tapping on said resistor.

4. Apparatus for providing a protective spark gap for a DC. powerline as claimed in claim 3, wherein said resistor means includes a second resistor connected between said spark gap means and earth, and said second main electrode carries a second trigger electrode which is connected to a tapping on said second resistor.

5. Apparatus for providing a protective spark gap for a powerline as claimed in claim 1, wherein blower means causes a draught of air to flow through said first gap.

6. Apparatus for providing a protective spark gap fora D.C. powerline, including a triggatron and spark gap means connected in parallel with one another between the DC. powerline and earth, the triggatron having a first main electrode connected to the DC. powerline and a second main electrode spaced from the first main electrode to provide a first gap therebetween and connected to earth, said first main electrode carrying a first trigger electrode adjacent to said first gap, said first trigger electrode being insulated from said first main electrode to provide a second gap therebetween, said second main electrode carrying a second trigger electrode adjacent to said first gap, said second trigger electrode being insulated from said second main electrode to provide a third gap therebetween, and resistor means connected in series with said spark gap means between the DO. powerline and earth, said first and second trigger electrodes being connected to a tapping on said resistor means, so that a flow of current across said spark gap means causes the DC. powerline to discharge to earth via first and second main electrodes.

7. Apparatus for providing a protective spark gap for a DC. powerline as claimed in claim 6, wherein said first and second trigger electrodes are mounted within said first and second main electrodes coaxial with the line joining the centres of said first and second main electrodes.

8. Apparatus for providing a protective spark gap for a DC. powerline as claimed in claim 6, wherein said resistor means comprises a single resistor.

References Cited UNITED STATES PATENTS 1,232,467 7/1917" Peek 317-61 1,477,306 12/1923 Allcutt 317--61 1,477,307 12/1923 Allcutt 31761 2,508,954 5/1950 Latour et al 313198 X 3,206,644 9/1965 Spindle 317-16 X 3,211,940 10/1965 Hueschen 313325 X FOREIGN PATENTS 825,899 12/ 1959 Great Britain.

LARAMIE E. ASKIN, Primary Examiner. 

